Method of manufacturing metal spheres



Jan. 13, 1942. 'J. GALLUP 7 2,269,528

METHOD OF MANUFACTURING METAL SPHERES Filed March 30, 1946 NO/VOX/D/Z/NG ATMOSPHERE INVEN TOR. JUHN L. GALLUP A TTORNE I".

- those obtained by sintering metal powers.

Patented Jan. 13, 1942 v UNITED STATES PATENVTP OFFICE.

Mrrrnon or'mmumcruamc METAL srneaas John L. Gallup, Newark, N. 1.,assigncr to Radio Corporation of America, a corporation of Delaware ' Myinvention relates to a method of manufacturing small metal spheres andparticularly to a method of making metal spheres of uniform size andshape.

In my U. S. Patent No. 2,175,689 I have disclosed an electrode of themosaic type suitable for use in television transmitting tubes. Theelectrode of the type described includes sintered metal particles orplugs mutually separated and insulated from a conducting foundation byan intermediate insulator. I have found that it is desirable to providedenser metal plugs than It is desirable that these metal plugs beuniform in size and shape but various methods of manufac-' turing suchsmall particles, which usually range in size from .01" to .005", havebeen found unsatisfactory. Small metal spheres are particu larly suitedto this use, but attempts to make small metal spheres by spraying themetal from a spray gun of the Schoop type or passing molten metalthrough a fine mesh screen as in the shottower process do not meet withsuccess. In the first method the particles produced are of nonuniformshape and size so that less than. 4% of the product is usable. In thelatter process the molten metal will not pass through a fine refractoryin character. feed the wire 2 into the melting region or flame with gasand air, although oxygen-and hydrogen may be used when melting certainmetals highly The rollers 3 preferably being such that the wire ismelted at the rate wire mesh screen but rather collects in large dropson the under side of the screen, the drops bearing no apparentrelationship to the size of the openings in the screen.

It is an object of my invention to provide a method of manufacturingsmall metal particles or spheres of uniform size and shape. It is afurther object of my invention to provide equipmerit for and a method ofmanufacturing metal spheres in which the percentage yield of the desiredsize range is increased. In accordance with my invention, I melt a metalwhich it is desired to make into small particles, allow the molten metalto fall a considerable distance through space and interrupt the fall onan inclined plane of resilient material to break the melted metal intosmall metal particles which are solidified and cooled. These and otherob-.

. interruption, the smaller the particle size.

burner 5. The burner 5 is preferably supplied 55 at which it is fed.After the wire is melted in the flame 4 the molten metal is allowed tofall through space for a distance determined by the size of the metalparticles desired, as will be referred tolater. If the metal is of sucha material as to be readily oxidized, the path of the falling moltenmetal may be surrounded by a tube 6 containing a non-oxidizingatmosphere which may enter the tube 5 such as through the inlet 1,.although I have found this to be unnecessary when making metal particlesof such metals as silver, copper, zinc, nickel or nickel chrome alloys.

' plane of the platform may be varied. The platform 8 supports a sheet 9of resilient material 'such as at its four corners so that the moltenmetal, when interrupted in its fall, will bounce from the resilientsheet 9, whereupon it may be collected and cooled such as by a waterbath I0.

I have found the size of the particles made of any given metal to bedependent upon a number of variables. Thus I have found that the hotterthe melting region, such as the flame 1, the smaller will be theparticles size. Likewise I have found that the greater the distance thatthe molten metal is allowed to fall before This distance may vary from 6inches to 8 feet when making silver particles, the only requirementbeing that the metal should be molten at the time it is interrupted bythe resilient sheet 9. The particle size may be further controlled byvarying the angle of incidence between the path of the falling metal andthe plane of the resilient sheet 9. Thus for grazing incidence I havefound the particles to be considerably larger than for angles nearer theperpendicular, although I have obtained the best results, both withrespect to the uniformity of particle size and the maximum yield ofspherical particles, when this angle of incidence is approximately 45. Ihave tried a number of materials for the purpose of interrupting thefall of the molten metal and have shown in the drawing.

The resultant product made in accordance with my invention are particlesof metal which are substantially spherical, the size of the parti-.

cles being quite uniform. In addition, my equipment and method areparticularly suited for making metal particles of other metals thansilver, such as copper, zinc, nickel and nickel chrome alloys. Formetals which ha e a tendency to oxidize while being melted, I prefer touse a reducing type flame to prevent the formation of oxide, but formetals such as zinc I have found that the use of an oxidizing flame isadvantageous.

While I have indicated the preferred embodiments of my invention ofwhich I am now aware and have also indicated only one specificapplication for which my invention may be employed, it will be apparentthat my invention is by no means limited to the exact forms illustratedor theiise indicated, but that many variations may be made in theparticlular structure used and the purpose for which it is employedwithout departing from the scope of my invention as set forth in theappended claims.

I claim:

1. Apparatus for manufacturing small metal particles comprising a sourceof metal to be melted, means to melt the metal into relatively largeparticles, said means being elevated so that upon melting the particlesof metal immediately drop through space, means to intercept theparticles which drop through space while the particles are still in amolten state, said means comprising an inclined base of heat insulatingnonmetallic resilient material of sufllcient thinness as to be flexibleunder the impinging particles causing the particles to rebound andsubdivide into smaller particles.

2. Apparatus for manufacturing small metal particles comprising means tomelt a quantity of metal, said means being elevated so that the metalfalls through space immediately upon becoming molten, a thin base ofresilient material of suflicient thinness as to be flexible under impactof said molten metal and positioned to intercept the falling moltenmetal and cause the metal to be subdivided into small particles, thebase being supported from its sides so that the impinged area of thebase is free to flex under the impact of said particles.

3. Apparatus for manufacturing small metal particles comprising aresilient non-metallic base capable of deformation by small moltenparticles impinging thereon, said base being inclined at an angle to thevertical and" supported from the edges thereof, means directly above anunsupported area of said base to melt a quantity of metal which whenmolten falls on the said area of said base and'means to collect and coolsaid metal following the impingement of said metal on said base causinga flexure thereof.

JOHN L. GALLUP.

